1. Field of the Invention
This invention relates to a lockable torque-limiting driver, particularly to one provided with a sleeve having its upper edge disposed with a plurality of positioning serrations, and a torque-limiting member having its upper side fixed with positioning projections. To adjust torque of the torque-limiting driver, a user only has to turn the torque-limiting member with fingers to let the male threads of the torque-limiting member engaged with the female threads of the sleeve and thus, by the number of sounds produced by the positioning projections moving on the positioning serrations, an adjuster is able to know a desired torque-limiting extent, needless to employ any external tool for adjusting torque of the torque-limiting driver and able to carry out adjustment quickly and accurately.
2. Description of the Prior Art
A first conventional torque-limiting driver, as disclosed in a U.S. Pat. No. 7,487,700B2, titled “LOCKABLE TORQUE-LIMITING DRIVER AND METHOD”, has an adjustment plug 60 and a locking plate 75 in a first preferred embodiment, or an adjustment plug 67 and a locking plate 80 in a second preferred embodiment, or an adjustment plug 67 and a locking plate 100 in a third preferred embodiment combined together. Thus, an adjuster can turn the locking plate together with the adjustment plug with fingers to change a combination extent between the adjustment plug and a sleeve 29 for carrying out adjustment of torque. After being adjusted, the torque can be kept unchangeable by having the serrations 79 OF the body-engaging portion 77 of the locking plate engaged with a pair of prongs 29A of the sleeve 29.
A second conventional torque-limiting driver, as disclosed in a U.S. Pat. No. 5,397,269, titled “TORQUE LIMITING CLUTCH AND ITS USES” has a closure block 76 secured at an inner side of the end of a housing 40. Thus, the locking torque of a driven member 50 can be decided by adjusting the extent that the closure block 76 is locked in the housing 40.
A third conventional torque-limiting driver, as disclosed in a U.S. Pat. No. 4,238,978, titled “TORQUE WRENCH”, has an adjusting screw 36 installed at a lower side of the main body of a housing. Thus, the locking torque of a socket tool 18 can be changed by adjustment of the adjusting screw 36.
The first conventional torque-limiting driver has torque-limiting means installed in the interior of a body so locking torque can be avoided being adjusted improperly, having an advantage that the equilibrium of locking torque can be achieved but a disadvantages that the torque-limiting means has to be disassembled in order to carry out torque adjustment. However, the second and the third conventional torque-limiting driver seen most frequently on the market can be freely adjusted by a user, unnecessary to disassemble the driver. But the first conventional torque-limiting driver has a complicated structure that the adjustment plug and the locking plate have to be produced independently and separately, increasing assembly work.